This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Toxoplasma gondii is an obligate intracellular parasite, highly prevalent in warm-blooded animals and capable of infecting any nucleated cell. Two forms characterize asexual replication of Toxoplasma gondii in humans and intermediate hosts: rapidly growing 'tachyzoites'and latent 'bradyzoite'tissue cysts. Tachyzoites are responsible for acute illness that has been associated with congenital neurological defects, while the more slowly dividing bradyzoite form can remain latent for years, and often manifests itself in immunocompromised hosts. These two developmental stages are essential for disease propagation and causation. We have developed a genetic screen to identify regulatory genes that control parasite differentiation and have isolated mutants that fail to convert to bradyzoites under differentiation conditions. The locus disrupted in one of these mutants (mutant B7) shows a reduced expression of a developmentally regulated transcript, named B41. B41 contains no obvious open reading frame. We hypothesize that this locus encodes a functional non-coding RNA that plays a critical role in bradyzoite formation. We are conducting experiments to determine if this ncRNA functions as a source of micro RNAs or functions as a large ncRNA (this transcript is 2.6 KB long and polyadenylated). We are using microarrays to examine possible relationships between B41 and other genes affected in mutant B7. We are carrying out experiments to functionally characterize the disrupted locus in mutant B7.